A master cylinder is utilized in a vehicle brake system to generate fluid pressure during a brake application. The fluid pressure is communicated to front and rear brake assemblies to effectuate braking for the vehicle. Generally, a housing includes a reservoir to retain the brake fluid and movably supports a pair of pistons to develop fluid pressure in a primary pressure chamber and a secondary pressure chamber. As one of the pressure chambers is in communication with the rear brake assembly it is desirable to proportion the communication of fluid pressure to this rear brake assembly to avoid rear wheel lockup during braking.
In the past a proportioning valve was responsive to the fluid pressure within the one pressure chamber to restrict fluid communication to the rear brake assembly in response to increasing fluid pressure therein. The proportioning valve was also disposed within one of the pistons as illustrated in my prior U.S. patent application Ser. Nos. 936,272, now U.S. Pat. No. 4,249,379 and 14,449, now abandoned, to incorporate the proportioning mechanism within the master cylinder, thereby saving space in an engine compartment.
In view of the number of parts disposed within the one piston and also because of the increasing reduction in the size of the one piston it is desirable to provide a master cylinder with a simple proportioning valve arrangement.